1. Field of the Invention
The present invention relates to a frictional engagement apparatus mounted, for example, in an automatic transmission for vehicle. In particular, it relates to the frictional engagement apparatus of small-size and light-weight.
2. Related Art
Conventionally, an automatic transmission for vehicle provided with plural planetary gear apparatuses and plural frictional engagement apparatuses has been known and practically used. In this automatic transmission for vehicle, plural rotary elements constructed through connection of the plural planetary gears are suitably engaged or released by the plural frictional engagement apparatuses to establish plural speed change ratios. With recent multi speed change ratios of the automatic transmission for vehicle, more planetary gear apparatuses and more frictional engagement apparatuses are mounted on the automatic transmission for vehicle. For example, the Patent Document 1 (Japanese Patent Application Laid-open No. 9-53691) discloses two clutch apparatuses as the frictional engagement apparatuses.
On the other hand, the more planetary gear apparatuses and the more frictional engagement apparatuses cause problems of large-size and heavy-weight of the automatic transmission for vehicle. To overcome such the problem, some techniques including the above Patent Document 1 for realizing the small-size and the light-weight have been developed.
FIG. 6 shows a conventional automatic transmission for vehicle 100 disclosed in the above Patent Document 1. The automatic transmission for vehicle 100 includes a clutch drum 102 and two sets of frictional engagement units 104 and 108. In detail, the clutch drum 102 has a drum shape and is commonly used for the two sets of frictional engagement units 104 and 108. Both the first frictional engagement unit 104 and the second frictional engagement unit 108 are disposed at an inner periphery of the clutch drum 102 and respectively include plural friction plates arranged axially.
In the first frictional engagement unit 104, plural friction plates 105 held by the clutch drum 102 and plural friction plates 107 held by a clutch hub 106 are alternately arranged. Similarly, in the second frictional engagement unit 108, plural friction plates 109 held by the clutch drum 102 and plural friction plates 111 held by a ring R are alternately arranged.
On an inner surface of the clutch drum 102, between the first frictional engagement unit 104 and the second frictional engagement unit 108, a stop ring 112 is held so as not to be shifted axially and not to be rotated circumferentially relative to the clutch drum 102. Commonly using the stop ring 112 for both the first frictional engagement unit 104 and the second frictional engagement unit 108 can shorten an axial length of the automatic transmission for vehicle 100.
In the frictional engagement apparatus of the Patent Document 1, as shown in FIG. 7, a first piston 114 disposed behind the first frictional engagement unit 104 pushes it. Thus, the friction plates 105 and the friction plates 107 are brought into contacted state, and the stop ring 112 is deformed toward the second frictional engagement unit 108. The deformation of the second frictional engagement unit 108 causes contact between the friction plates 109 and the friction plates 111, so that these friction plates 109 and 111 may be deteriorated in durability thereof. For this reason, improvement for avoiding such unexpected contact of the friction plates 109 and 111 has been required.
On the other hand, when a piston 116 pushes the second frictional engagement unit 108, the stop ring 112 deforms toward the first frictional engagement unit 104 to deteriorate durability of the friction plates 105 and the friction plates 107.